Under the circumstance such that decoding of the whole base sequence of human genome is terminated and decoding of base sequence for genome of other living organisms is in breakthrough, a huge amount of base sequence information is being accumulated. It seems that a gene-related technology will be dramatically developed in a wide range of fields such as diagnosis of various diseases, development of medicaments, breed improvement of agricultural products by revealing the function of gene in the living organisms on the basis of the genome base sequence information. A base of such development of the new field is information on gene expression and function in addition to the base sequence information. DNA chip or DNA microarray (hereinafter referred to as “DNA microarray” as a generic nomination of both) has been developed as a technology for performing a large scale decoding of the gene function and the gene expression and leading the same to the genetic screening. However, many of the DNA microarrays in the status quo are based on a principle of fluorescence detection. It has problems that laser or complex optical system is required, and the system is upsized and expensive.
Most of the currently developed DNA microarrays are based on a principle of detection of double strand DNA on the basis of hybridization and selectivity of reactions is not very high. Therefore, there is a problem in accuracy of the gene polymorphism analysis. In particular, in the field of medical practice, it is necessary to detect gene polymorphism or Single Nucleotide Polymorphism (hereinafter, it may be abbreviated as SNP) simply in high degree of accuracy for realization of a tailor-made medical practice. Therefore, a technology which can satisfy increase of both simplicity and accuracy has been required.
As a method of resolving these problems, some DNA microarrays of a current detection system which is combined with an oxidation-reduction indicator are reported. For example, there is developed a system for detecting a target gene by fixing an end of a molecule denominated as molecule wire to a metal electrode, hybridizing a nucleic acid probe to the other end thereof, and the detecting oxidation-reduction indicator and giving receiving of electrons of metal electrode as variations in electric current on the basis of hybridization with respect to the target gene (Non-Patent Document 1 and Non-Patent Document 2).
There is also developed a system for detecting hybridization by measuring the oxidation-reduction current at the metal electrode using Ferrocenylnaphthalene Diimide as an electrochemically active indicator (Non-Patent Document 3). There is further developed a medicinal virtue inspection system for hepatitis C using a current detection system DNA tip (Non-Patent Document 4). In this system, an expensive laser, a complex optical system or the like are not necessary, a simple and compact system can be established.
However, in the case of the four systems in Non-Patent Documents 1 to 4, since detection is based on the oxidation-reduction reaction on the metal electrode in principle, there is a problem such that if there exists an oxidizing substance or a reducing substance in a sample (for example, ascorbic acid), an electric current based on oxidation or reduction flows, which hinders detection of gene and results in deterioration of detection accuracy. In association with measurement of the electric current, electrode reaction is proceeded on the metal electrode. Since the electrode reaction is irreversible and non-equilibrium reaction, corrosion of the electrode or generation of gas may be resulted, and consequently, separation of immobilized nucleic acid or impairment of stability of current measurement may be resulted. Therefore, there is a problem such that the detection accuracy may be deteriorated specifically when measurement is repeatedly performed.
There is also reported a trial to detect the hybridization of DNA using the field-effect device (Non-Patent Document 5). This technology is for detecting a change in electric charge by hybridization using the field effect on the basis of the fact that the DNA molecule has a negative electric charge in solution. However, since the DNA probe formed on a substrate has the negative electric charge by nature, the amount of change in electric charge by the hybridization of the target gene is small, and hence identification from non-specific adsorption is impossible. Therefore, increase in sensitivity and improvement of accuracy have been subjects to be solved for genetic screening. It is also difficult to detect a slight difference (one base is different) between two genes such as the Single Nucleotide Polymorphism (SNP) since both the sensitivity and accuracy (selectivity) are low.
Non-Patent Document 1: Nature Biotechnology, vol. 16, p. 27-31, 1998
Non-Patent Document 2: Nature Biotechnology, vol. 16, p. 40-44, 1998
Non-Patent Document 3: Anal, Chem, 72, p. 1334-1341, 2000
Non-Patent Document 4: Intervirology, 43, p. 124-127, 2000
Non-Patent Document 5: J. Phys. Chem. B., 101 p2980-2985, 1997